1. Technical Field
The present invention relates to a signal synchronization method and a signal synchronization circuit.
2. Related Art
Generally, a technique has been known which uses a synchronization circuit for outputting data transmitted from a transmitter to a receiver by synchronizing the data with the clock signal of the receiver when devices, which are respectively operated by clock signals of different periods, exchange data (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-71221).
However, some processors change a request signal from an inactive state to an active state when requesting the exchange of data, but do not change the request signal into the inactive state and maintain the active state when successively issuing the subsequent request. In such a case, a problem arises in that the subsequent request is not detected although the synchronization circuit synchronizes the request signal with the clock signal of the receiver. As examples of this case, FIG. 5A shows a configuration of a synchronization circuit 100 having shift registers in two stages, and FIG. 5B shows the relationship between a request signal of a processor input to the synchronization circuit 100 and an output from the synchronization circuit 100. In FIG. 5B, the processor causes the request signals to rise at time t0 and change from an inactive state to an active state, and issues the subsequent request so as to maintain the active state of the request signal at time t3. In this case, in response to the first request, the output of the synchronization circuit 100 rises at time t2 and the inactive state is changed to the active state by the rising edges of the clock signal of the receivers two times at time t1 and time t2. Hence, the receiver is able to detect the request issued from the processor. However, in response to the subsequent request at time t3, the output of the synchronization circuit 100 will rise at time t5 similarly to the previous request, but the active state based on the first request is continuously maintained ahead of time t5. Therefore, there is no change in the output, and thus the receiver is unable to detect the subsequent request.